Some AMD Athlon 64 Linux Desktops and Laptops suffer from what is known as the "50% CPU Utilization when idle", and "Clock running twice as fast" issues. After a fresh Linux install, the system clock will run twice as fast as normal, and monitoring the CPU utilization will report 50% utilization when the computer is idle. This issue has been known to happen on the HP Pavilion zv6000 series, the Compaq Presario R4000 series and other AMD Athlon 64 based laptops and desktops running the 64 bit version of Fedora Core 4, Ubuntu, Gentoo, SUSE and other 64 bit Linux distros.
To fix the problem, the no_timer_check parameter must be passed to
the kernel. To accomplish this, look for a line similar to the following
kernel /boot/vmlinuz-2.6.12-1.1398_FC4 ro root=LABEL=/1
kernel /boot/vmlinuz-2.6.12-1.1398_FC4 ro root=LABEL=/1 no_timer_check
Save the file, reboot, the clock should now work properly, and the CPU utilization will be at or close to 0% when idle, just like it should be.